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Development of Non-Proprietary UHPC Mix (University of Oklahoma)

Deterioration of bridges can often be related to poor performance of longitudinal connections or transverse deck joints, which can be more frequent when precast panels are used for accelerated bridge construction. Ultra-high performance concrete (UHPC) is a relatively recent advancement in cementitious composite materials with mechanical and durability properties far exceeding those of conventional concrete. It combines a high percentage of steel fibers with an optimized gradation of granular constituents, resulting in a compressive strength in excess of 22 ksi, a high post-cracking tensile strength, and exceptional durability. The short reinforcing bar development lengths and exceptional durability provided by UHPC lead to great potential for use in bridge deck joints, other applications for accelerated bridge construction, and as a repair material. The long-term benefits of using UHPC in a number of applications are evident, but commercially available proprietary mixture formulations are very expensive and mix design using local materials is much more complicated than for conventional concrete. The material characteristics, complicated mix design, and need for specialized mixing procedures require detailed specifications and quality control testing currently not included in most states’ standard specifications. Guidance for UHPC produced with local materials that can achieve the necessary mechanical properties and durability for use in bridge component connections is needed to provide additional options for DOTs.
All ABC-UTC partner institutions are considering the use of UHPC for bridge deck joints and a number of other applications, but coordinated efforts are needed to understand the repeatability and impact of locally available materials on performance of non-proprietary UHPC mixture formulations. A mix design developed in one part of the country may not directly translate to another region of the country if the constituent materials used for the mix are not exactly the same. Examination of material properties for UHPC made with constituent materials from different regions is needed to provide guidance applicable for the entire United States. Furthermore, steel fibers are typically the most expensive component of the UHPC mix and also have a significant impact on structural behavior of UHPC. A more thorough understanding of the impact of different fiber contents on non-proprietary UHPC performance could allow for different mix designs with an optimum fiber content tailored to properties required for specific applications.
The primary objective of the project is to develop guidance for an “ABC-UTC Non-Proprietary UHPC Mix” design produced with local materials that can achieve the necessary mechanical properties and durability for use in bridge component connections. The five ABC-UTC partner institutions will coordinate efforts to examine material properties, reinforcing bar development length, shear behavior, full-scale joint behavior, and durability of the “ABC-UTC Non-Proprietary UHPC Mix.”